Metal or metal oxide particles of submicron size are a valuable industrial commodity finding use in many applications including for example in the manufacture of industrial catalyst such as might be employed in the chemical industry, in the manufacture of ceramics, of electronic components, and as fillers for, for example, plastics, paints or cosmetics.
A large variety of techniques are available for the manufacture of metal or metal oxide powders having a very fine particle size. Such techniques include solution processes and high temperature gas phase and condensed phase syntheses. For a comprehensive review of the general techniques available reference is made to the recent publication entitled "Chemical Engineering Aspects of Advanced Ceramic Materials" by V. Hlavacek and J. A. Puszynski published in the Journal of Industrial Engineering and Chemical Research, pages 349-377, Volume 35, 1996.
Despite the numerous procedures available a problem in common to a lesser or greater extent with nearly all methods is the difficulty of obtaining consistently fine uniform particles of good purity and strength. Procedures that can provide a greater consistency in this respect invariably have high costs associated with their operation due to the complexity of the equipment required, the use of expensive raw materials, or high energy consumption. It would therefore be desirable to develop a cost effective procedure leading to the production of metal or metal oxide powders having a consistently fine particle size. It would be of particular advantage if such a procedure could be operated using raw materials readily available and could be operated in the substantial absence of highly specialized equipment and costly solvents or chemical processing aids. It would also be an advantage if such a procedure were able to provide for the production of metal powders in a more attractive yield.
A common objective is the production of a metal powder that has a fine particle size and does not exhibit the problem of agglomeration leading to a wide particle size distribution. To optimize this, it is necessary to develop a process which provides a homogeneous and even distribution, precipitation, of the metal-containing substance in the first instance without providing subsequent opportunity for secondary nucleation leading to agglomeration. With this in mind, laboratory studies have been undertaken to evaluate the use of reactive polymer chemistry in providing the desired homogeneous distribution starting from an aqueous metal salt solution. The reactive polymer of choice is polyurethane; the basic polyurethane reactive components comprising polyisocyanate are commercially available at low cost and exhibit compatibility with water. Patent publications which disclose the manufacture of polyurethane polymer containing metal particles or metal salts and the subsequent calcining or pyrolysis of the resulting polymer include U.S. Pat. Nos. 3,510,323; 4,569,821; and 5,338,334; and the published French Patent application 2,609,915. These documents do not meet the particular needs outlined above.